Conventional diesel cycle engines in use today for vehicular and other industrial uses are fueled by a high grade fuel oil known as "No. 2 grade" and as "diesel fuel." It is a petroleum based fuel, high in hydrocarbons, has good lubricity characteristics which assists in lubricating the injectors and other moving parts exposed to the fuel prior to its being introduced into the combustion chamber, and is ignitable (with or without the assist of a glow plug) at relatively low compression ratios ranging up to as much as 19:1.
However, with the advent of concern over reducing hydrocarbons and other combustion by-product emissions into the environment, there has been increased design effort in maximizing the performance characteristics of this fuel. Some have been cost effective, i.e. higher performance, greater thermal efficiencies. Others have not, i.e. the addition of catalytic convectors.
Coincident with these concerns, has been the concern of petroleum-based fuel shortages and the need for alternative fuel sources. Among these considered are methanol and ethanol, which are low cetane liquid fuels, and natural gas which is a low cetane gas. Methanol is a particularly attractive fuel alternative since it is a liquid fuel, therefore, compatible with known liquid fuel systems, and it is a by-product of natural gas which is an abundant energy source. However, the special properties of methanol require major changes in engineering design in the engine and the air supply and fuel systems for the engine, to name a few.
Some of these changes, namely those dealing with the air supply are dealt with in U.S. Pat. No. 4,539,948 (Toeppel), assigned to the assignee of the present invention. It describes a two-cycle diesel engine for handling methanol fuels whereby the scavenging, i.e. that which sweeps the combustion chamber immediately following combustion to clear the exhaust gasses from the combustion chamber, is controlled to allow that a certain amount of hot residual gasses will remain in the combustion chamber to thereby support the auto ignition of the methanol fuel during the next power cycle.
Despite these and other prior efforts, until the present invention, there was no two-cycle diesel engine in use, fueled solely by methanol or any other low cetane liquid fuel. Nor has there been developed a fuel system which is completely compatible with the unique characteristics of a fuel such as methanol and which offers satisfactory, long-range durability and performance. The present invention is directed to those major remaining concerns.